1. Field of the Invention
The present invention relates to novel aqueous dispersions based on silicones that are crosslinkable into flame-resistant elastomeric state by elimination of water therefrom.
2. Description of the Prior Art
Aqueous silicone dispersions that are crosslinkable into elastomeric state by elimination of water therefrom are known to this art; these comprise:
(a) an emulsion (A), of the oil-in-water type, of an .alpha.,.omega.-(dihydroxy)polydiorganosiloxane stabilized by an anionic and/or nonionic surfactant; PA1 (b) a crosslinking agent; PA1 (c) a non-siliceous inorganic filler material; and PA1 (d) a hardening or curing catalyst. PA1 (i) a microemulsion of silsesquioxane resin (U.S. Pat. No. 3,355,406); PA1 (ii) a siliconate (EP-A-266,729 and EP-A-332,544 and Application EP 89/4,203,785, filed Oct. 9, 1989 and assigned to the assignee hereof); PA1 (iii) a reactive silicone resin of low molecular weight containing alkoxy or acyloxy groups (U.S. Pat. No. 4,554,187); PA1 (iv) a silicone resin of high molecular weight, insoluble in toluene (EP-A-304,719); PA1 (v) a polyalkoxysilane, a polysilicate, a polyacyloxysilane or a polyketiminoxysilane (U.S. Pat. Nos. 3,294,725, 4,584,341, 4,618,642 and 4,608,412); PA1 (vi) a polyamino (or amido)silane (Application FR-A-89/01,654, filed Feb. 3, 1989 and assigned to the assignee hereof); PA1 (vii) a polyalkenoxysilane (Application FR-A-88/13,618, filed Oct. 11, 1988 and assigned to the assignee hereof); and PA1 (viii) a hydroxylated silicone resin containing, per molecule, at least two siloxy units selected from among those of the formulae: R.sub.3 SiO.sub.0.5 (M), R.sub.2 SiO (D), RSiO.sub.9.5 (T) and SiO.sub.2 (Q) (French Application FR-A-88/11,609, filed Aug. 31, 1988, and also assigned to the assignee hereof). PA1 (a) a stability on storage for at least 6 months and preferably at least one year; PA1 (b) a satisfactory adherence to very diverse supports, stone, concrete, mortar, metals, steel, aluminum, fibrocement, enamels, ceramics, etc.; PA1 (c) a viscosity suitable as to be extrudable from the packaging cartridge and suitably film-forming; PA1 (d) a suitable resistance to abrasion, in particular to moist abrasion, to atmospheric humidity, and to actinic radiation (visible light, U.V.); PA1 (e) a reasonable shrinkage after crosslinking and evaporation of water; PA1 (f) a good permeability to gases and to water vapor; PA1 (g) satisfactory mechanical properties, in particular in respect of modulus of elasticity and tear strength; and PA1 (h) a satisfactory water-repellency. PA1 (A) 100 parts by weight of an emulsion, of the oil-in-water type, of an .alpha.,.omega.-(dihydroxy)polydiorganosiloxane, stabilized by at least one surfactant selected from the anionic and nonionic surfactants and mixtures thereof; PA1 (B) an effective amount of at least one crosslinking agent; PA1 (C.sub.1) 5 to 100 parts by weight, preferably 20 to 80, of a non-siliceous inorganic filler; PA1 (C.sub.2) 5 to 100 parts by weight of borax hydrate powder; and PA1 (D) optionally, 0.01 to 3 parts by weight of a catalytic hardening metal compound, said dispersion having a solids content of at least 40% by weight. PA1 (i) 0.1 to 15 parts, preferably 1 to 10 parts, of an organosiliconate; PA1 (ii) 1 to 100 parts of a microemulsion of silsesquioxane resin according to U.S. Pat. Nos. 3,355,406 and 3,433,780; PA1 (iii) 5 to 100 parts of a reactive silicone resin of low molecular weight containing alkoxy and acyloxy groups, PA1 (vi) 5 to 100 parts of silicone resin of high molecular weight which is insoluble in toluene; PA1 (v) 5 to 100 parts of a hydroxylated silicone resin containing, per molecule, at least 2 different structural units selected from among those of the formulae: R.sub.3 SiO.sub.0.5 (M), R.sub.2 SiO (D), RSiO.sub.1.5 (T) and SiO.sub.2 (Q), with R principally being a C.sub.1 -C.sub.6 alkyl, vinyl and 3,3,3-trifluoropropyl radical, and a hydroxyl group content by weight of from 0.1% to 10% (among such resins, which are preferably introduced in the form of aqueous emulsions, the resins MQ, MDQ, TD and MTD are particularly exemplary); and PA1 (vi) 1 to 20 parts of a silane of the formula: EQU R.sub.a SiX.sub.4-a PA1 (i) borax decahydrate, also termed disodium tetraborate decahydrate, of the formula: EQU Na.sub.2 B.sub.4 O.sub.7.10H.sub.2 O PA1 (ii) borax pentahydrate, also termed disodium tetraborate pentahydrate, of the formula: EQU Na.sub.2 B.sub.4 O.sub.7.5H.sub.2 O PA1 (iii) borax tetrahydrate, also termed kernite or Rasorite, namely, disodium tetraborate tetrahydrate, of the formula: EQU Na.sub.2 B.sub.4 O.sub.7.4H.sub.2 O PA1 (i) a mica hydrate such as expanded or nonexpanded vermiculite, PA1 (ii) ammonium aluminum sulfate dodecahydrate: EQU NH.sub.4 Al(SO.sub.4).sub.2.12H.sub.2 O, PA1 (iii) chromium sulfate pentadecahydrate: EQU Cr.sub.2 (SO.sub.4).sub.3.12H.sub.2 O, PA1 (iv) sodium sulfate heptahydrate: EQU Na.sub.2 SO.sub.4.7H.sub.2 O, PA1 (v) potassium chromium sulfate decahydrate: EQU Kr.sub.2 (SO.sub.4).sub.2.12H.sub.2 O, PA1 (vi) tetrasodium pyrophosphate decahydrate: EQU Na.sub.4 P.sub.2 O.sub.2.10H.sub.2 O, PA1 (vii) calcium oxide hexahydrate: EQU CaO.8H.sub.2 O, PA1 (viii) trisodium orthophosphate decahydrate: EQU Na.sub.3 PO.sub.4.10H.sub.2 O, PA1 (ix) zeolite hydrate. PA1 The catalytic hardening metal compounds (D) are essentially the salts of carboxylic acids and halides of such metals as lead, zinc, zirconium, titanium, iron, tin, barium, calcium and manganese. PA1 The constituent (D) is preferably a catalytic compound containing tin, generally an organotin salt, preferably introduced in the form of an aqueous emulsion. The organotin salts which are suitable are described, in particular, in the publication by Noll, Chemistry and Technology of Silicones, page 337, Academic Press (1968).
The base emulsion comprises a silicone oil having silanol endgroups, which is generally emulsion-polymerized as described in U.S. Pat. Nos. 2,891,920, 3,294,725 and 3,360,491, namely, using an anionic surfactant which, preferably, also serves as a polymerization catalyst.
In this type of aqueous dispersion, a wide variety of crosslinking agents therefor are also known to this art, with the following being representative:
These known aqueous dispersions are typically catalyzed by a catalytic hardening compound which is, preferably, a tin salt or a combination of a tin salt and boric acid (FR-A-2,621,921).
Such aqueous dispersions are stable in storage for at least one year when they are sealedly packaged as a single component, in particular in a cartridge. They are extrudable and in this case are either flowing or non-flowing.
Pasty silicone elastomer compositions packaged in two components, where appropriate crosslinking in the form of a foam in the presence of platinum and having a high flame-resistance, are also known to this art (U.S. Pat. No. 4,433,069).
These elastomer compositions, which are not packaged in the form of aqueous dispersions, are effective, but present the disadvantage of being expensive and difficult to use.
EP-A-230,831 describes a flameproofing agent other than platinum for the same type of compositions. According to this '831 patent, at least 3.5 parts by volume of a flameproofing agent comprising a mixture of borax decahydrate, aluminum hydroxide and silica is added to one part by volume of the silicone elastomer composition, the minimum amount of silica being at least two parts by volume.
FR-A-2,632,866 describes the addition of a mixture of treated TiO.sub.2, borax and vermiculite to a silicone elastomer.
Flameproofing agents have also been proposed to this art for aqueous dispersions of silicone oils crosslinkable into an elastomer by elimination of water; FR-A-2,621,921 thus describes the use of aluminum hydroxide.
EP-A-332,544 describes the concomitant use of aluminum hydroxide and expanded or non-expanded vermiculite.
EP-A-212,827 describes the concomitant use of expanded vermiculite and fibers selected from ceramic fibers and aramide fibers.
The major disadvantage presented by the elastomers which are the subject of these latter three patents, is that, after they have been exposed to an open flame, the burned elastomers no longer have any mechanical properties because they have become a friable solid without any cohesion.